1. Field of the Invention
This invention relates to improvements in filter circuitry for use in conjunction with alternators of the type used in automotive or vehicular applications, and, more particularly, to improvements in methods and apparatuses for filtering the ripple in a multi-phase alternator in a vehicle system employing synchronous sampling techniques.
2. Description of the Prior Art
Most modern automobile and vehicle electrical systems employ alternators driven by the vehicle engine to source electrical energy for the electrical circuitry of the vehicle, as well as to charge the battery of the vehicle. Typically, the output of an alternator is a three-phase, AC signal that is rectified by a trio of diode pairs. The resulting output to the vehicle has a ripple associated with it. The ripple causes several problems in the vehicle, the most obvious of which is a whine in the radio when tuning very weak stations. The ripple also causes problems for the alternator voltage regulator. The output voltage from the alternator is generally specified to accuracies of 0.1 volts or so, but the ripple can be higher than 5 volts in American cars, and higher still in European applications, especially where the battery is in a remote location such as the trunk of the vehicle.
A major problem encountered in voltage regulator designs is filtering the ripple to enable the actual system voltage to be accurately sensed. The normal approach is to use an analog low pass filter, requiring at least a capacitor external to the integrated circuit performing sensing and regulation functions. Most regulators are mounted directly to the alternator, and are therefore located in a very hostile environment from a temperature and vibration point of view. Such conditions demand that a minimum number of components be used for best reliability.